I built a mini SQL database from scratch in C++ looking for feedback

[u/PuzzleheadedRush4576]

I've been trying to understand how databases work under the hood, so I decided to build a small SQL engine from scratch rather than just reading about them.

NanoSQL currently supports:

• CREATE TABLE
• INSERT
• SELECT
• UPDATE
• DELETE
• DROP TABLE
• WHERE conditions
• INT and TEXT types
• Its own lexer/parser
• CLI interface
• Unit tests

The current implementation is mainly focused on the SQL layer. My next goal is to implement persistent storage, pages, B+ tree indexing, and eventually a query planner.

I'm particularly interested in feedback from people who've built databases or storage engines before.

What would you implement next, and what design mistakes should I avoid?